The present invention relates generally to the field of automated apparatus for handling electronic circuit components and, more particularly, to automated apparatus for use in the art of burning-in circuit components prior to their distribution and use. Still more particularly, the present invention is directed to the art of automated insertion and removal of electronic integrated circuit (IC) packages into and out of sockets on printed circuit (PC) boards, and to the art of testing burn-in boards.
According to present practices, IC packages are mass-produced and installed in electronic circuits within highly sophisticated, complex, and costly equipment. As with many mass-produced products, IC packages are prone to failure, in some cases within the first one thousand hours of operation. The complexity of equipment within which such packages are installed makes post-installation failures highly undesirable. For example, when equipment reaches the final inspection stage of production, before failures are detected, the high level skills required for inspection and repair add a significant cost to production expenses. Even more significantly, when the product has been installed in the field and a service technician must make warranty repairs, the costs thereby incurred can have a significant effect on profitability. More and more often, however, post-installation failures simply cannot be tolerated because the potentially disastrous consequences. As a result, manufacturers of electronic equipment are demanding ever greater quality and dependability in commercial grade IC packages.
Quality and dependability are enhanced substantially by early detection of those IC packages likely to fail in the first few hours of operation, prior to the installation of packages in electronic equipment. One of the methods for detecting flawed IC packages is referred to generally as "burn-in". According to burn-in techniques, IC packages are stressed within their physical and electrical limits prior to installation, whereby those packages likely to become early failures in completed equipment can be discovered.
Burn-in involves placing a large number of IC packages on one or more PC boards ("burn-in boards"); placing the burn-in boards with the packages mounted thereon in a chamber whose environment, particularly temperature, is controllable; applying direct current (dc) biases to each package on each board in such a manner as to forward and reverse bias as many of the package's junctions as possible, and/or actively clocking each package to its maximum rated conditions, such application of dc biases, clock signals, and loads being accomplished substantially simultaneously to each package; removing the component boards from the chamber after the IC packages have been subjected to the environmental condition of the chamber and the biases, clock signals, and loads for a designated period of time; and removing the IC packages from the burn-in boards.
The IC packages can be electrically tested either within or outside the burn-in chamber, depending on the sophistication of the particular chamber, by applying a room temperature test of critical dc parameters, e.g., input currents and thresholds, output voltages and currents, and, in the case of digital components, by making a functional test to verify truth table performance. In this way, the packages that fail during burn-in are detected and segregated from those that do not fail.
Because the packages that do not fail during the burn-in process have withstood substantial stress, such IC packages possess a high degree of dependability and can be installed in highly complex equipment with reasonable confidence that such IC packages will not fail prematurely.
A second method for improving the quality control of IC packages (sometimes performed as a part of burn-in) is to verify that the IC packages function properly according to their minimum rated electrical operational specifications. Typically, after or during "burn-in", each IC package is tested across a broad range of parameters and, in some cases, graded as to its performance. Thereafter, the IC packages may be sorted into groups according to the performance grades.
The burn-in and test processes, however, although successful in reducing expenses associated with flawed IC packages, are not themselves without expense. Substantial capital expenditures are necessary to purchase or to construct burn-in chambers, burn-in boards, and test equipment. Personnel must be employed and trained to operate the equipment and to monitor the time-consuming processes. So substantial are the investments that independent businesses provide burn-in and test services to a variety of manufacturers. Cost effectiveness of the burn-in and test processes is therefore essential.
One means for improving the cost effectiveness of the burn-in and test processes is to reduce labor expenses and to improve efficiency and quality control through the use of automation. Accordingly, efforts have been made by the assignee of the present application and others to automate various aspects of the burn-in process. For example, assignee's U.S. Pat. No. 4,567,652, which is expressly incorporated herein by reference, discloses an apparatus for receiving IC packages from storage tubes and for loading the packages into sockets on a burn-in board for subsequent burn-in and test. In addition, assignee's U.S. Pat. No. 4,584,764, which also is expressly incorporated herein by reference, discloses an apparatus for unloading IC packages from burn-in boards subsequent to burn-in and test and, if desired, for sorting tested IC packages according to performance grades.
The advantages of automated loading and unloading of IC packages are well known. Automated handling enables the use of a computer to track and document the progress of each IC package through the burn-in process. In situations involving a high volume of IC packages for burn-in, automated handling equipment may be used to achieve a higher throughput of IC packages more efficiently than could be achieved otherwise. A single automated loader, for example, can easily replace eight or more very efficient employees assigned to the tedious task of loading burn-in boards. In any situation, automated handling equipment provides improved reliability and consistency of work product. Automated handling equipment, however, is generally very expensive.
Automated burn-in board loaders, unloaders, and testers, because of the distinctly different nature of their operation, generally are sold as independent units, any one of which may costs from $20,000 to $50,000 or more. The substantial nature of the capital investment required for purchase of this equipment, in spite of the known advantages of its use, represents an impediment to its purchase by even large manufacturers. Accordingly, there exists a need in the art for reasonably priced automated handling equipment. One means by which this end may be accomplished is to design an improved apparatus which, in spite of the distinctly different nature of loaders, unloaders, and testers, combines the three functions in a single, efficient machine.